One thing to note is that (as I understand it) sword fighting was never a thing, outside of dueling. In wars, the principal weapons were spear and bow (regardless of whether we’re talking about Japan or Europe). In the case of Europe, as heavy armor came into being, clubs and warhammers gained some popularity, but outside of that, it mostly comes down on spear and bow.
The sword existed in much the same capacity as a handgun. It’s something that one can carry in town, on your hip, that you can use to assert your position and keep the peace against unarmed peasantry.
In a pinch, if you lost your spear in battle, you would pull and use your sword. But you’d much rather keep your spear as it has greater reach and is much easier to use in formation. You can’t keep guys in formation very well if they need to hack about with a sword, and spreading your guys out is a good way to have them be taken out one by one by a formation of guys with spears.
So just like a sword is a stand-in for a handgun, a spear is a stand-in for a rifle. Hollywood and stage prefer handguns and swords, but in actual fighting, that’s not what’s used except as a fallback weapon.
From what I have experienced in Kendo and Fencing, if you’re in a fight with just swords (which would largely be the case in Japan), then the winner is whoever can best predict what the other guy was going to do. It’s like playing paper-rock-scissors. If you can correctly anticipate how the other guy is going to come at you, you can intercept and then chop through him. An actual fight would probably take less than 2 seconds. And a highly skilled fighter might chop through a whole load of other guys, simply because he’s really good at that sort of anticipation. Speed and dexterity probably had less to do with anything.
If you add a shield in, then - as I’ve heard others describe - things can get a bit more wrestling-like. The sword is a pricey item and if you break it, you’re boned. At least with a spear, if the head comes off, you’ve still got a functional quarterstaff. But if you break your sword, you’re out of luck. Similarly, if you get the sword lodged in the shield or the guy knocks the sword out of your hand, because you only have a single hand gripping it, you’re out of luck. So you end up at a mild stand-off where you don’t want to commit your weapon, and the only solution is to try and force an opening. Thus you end up with a lot of brute force ramming into one another, feints, and other play to get their shield out of the way.
I’d venture to guess that fights like these could either look like stand-offs or moshing depending on the participants and their style.